1. Field of the Invention
The present invention relates to a method of controlling the ignition timing of an engine and a system therefor. More particularly, this invention relates to a method of and system for controlling the ignition timing of a spark ignition type engine (hereinafter referred to as an "engine") mounted on a motor car and capable of to an optimum value in accordance with the operating condition of the engine.
2. Description of the Prior Art
In general, the ignition timing of an engine renders considerable effects to the output, fuel consumption and the like of the engine. Consequently, heretofore, the operating conditions of the engine, such as the rotational speed, and negative pressure in an air intake pipe, are detected and at the optimum timing predetermined in accordance with the values thus detected. Furthermore, as for other control factors such as the exhaust gas recirculation rate, cooling water temperature and the like, corrections have been made to the ignition timing commensurate with the values detected so as to optimize ignition timing. However, this method is disadvantages that the effects of atmospheric pressure, ambient temperature and other temperatures cannot be corrected for, without the addition of a multiplicity of sensors to detect all these factors. Further, optimum ignition timing change due to factors difficult to detect, such as changes with time due to mechanical wear of the engine, changes in the quality of fuel and the like. With the prior art ignition timing control method, it has been difficult to optimize ignition timing in view of the above-described factors. Consequently, losses in fuel consumption and output have been expected from the undetectable disturbances. For example, FIG. 1 shows the relationship between the humidity and optimum ignition timing. The optimum ignition timing varies up to a crank angle of 7.degree.-8.degree. depending upon the ambient conditions during use, and performance deteriorates therefrom. Furthermore, with respect to changes with time, the optimum ignition timing may vary by a crank angle of 15.degree.-20.degree. from the initial optimum ignition timing in accordance with the initial operating condition of the engine and the standard atmospheric condition, and a loss in fuel consumption up to about 10-20% has been expected therefrom. However, heretofore, there has been no countermeasure to eliminate the loss.
It has been proposed to detect fluctuations in torque from an output of an alternator or from acceleration in the rotational speed of the engine, whereby the ignition timings are feedback-controlled, as shown in U.S. Pat. No. 3,142,967. However, a sensor for detecting torque fluctuations from the alternator or an output shaft of the engine becomes complicated in arrangement, thus causing lowered reliability to the sensor.
Additionally, the ignition timing may be controlled in accordance with the amplitudes of the vibrations of the engine block caused by the fluctuation in torque of the output shaft or rotational vibrations about the output shaft. However, the operating condition of the engine and the external noises, such as vibrations of the vehicle, may render adverse effects to the method and the system therefor.